The present invention is directed to gas generators and to methods of generating a gas. In particular, the invention is directed to gas generators that may be used in any application requiring the relatively rapid generation of a gas, such as, e.g., inflation devices, fire suppression devices, and propulsion devices.
Gas generators are useful in many applications, including the inflation of inflatable objects, such as, e.g., aircraft escape slides, life rafts, and vehicular passive restraints, i.e., air bags and inflatable seat belts. Gas generators are also used as propulsion devices, such as rocket and jet engines, which release a large quantity of hot gas at high speed, producing thrust. Gas generators have also been found to be useful as fire extinguishers and fire suppression devices.
There are three generic types of gas generators: pressurized gas, pure pyrotechnic, and hybrid. Pressurized gas gas generators produce 100 percent of the generated gas from a stored pressurized gas, while pyrotechnic gas generators produce all of the gas from the combustion of a solid, liquid, or gaseous pyrotechnic material. Hybrid gas generators use the combustion of a pyrotechnic material to heat and expand a pressurized gas, and may produce a portion, typically from less than 10 percent to over 90 percent, of the generated gas from combustion products produced by the combustion of the pyrotechnic material.
Pressurized gas gas generators provide the coolest gas, and have a gas flow rate that can be regulated with time. Pressurized gas generators, such as, e.g., carbon dioxide fire extinguishers, typically comprise a tank containing a compressed or liquefied gas, a valve to maintain the compressed or liquefied gas within the tank during storage and for releasing the gas when needed, an outlet, and means for directing the released gas, such as a nozzle or conduit. As a result, pressurized gas gas generators tend to be large and heavy, and are often expensive. In addition, as a gas cools as it expands, pressurized gas gas generators may freeze up before all of the gas is released. Where the gas is carbon dioxide, a substantial portion of the gas may not be released, as the gas becomes sufficiently cold to produce solid dry ice within the tank. The storage temperature of the gas generator can also have a large effect on pressure of the stored gas, as the pressure of the gas varies directly with the absolute temperature of the gas. For example, the pressure of a given volume of gas at 0xc2x0 C. is only about 73 percent of the pressure of the same volume of gas at 100xc2x0 C. As a result, the rate of gas generation is significantly reduced at low temperatures, and is significantly increased at high temperatures. In addition, a gas generator designed to produce a given pressure of gas at a given temperature will produce a lower pressure of gas for the same volume at low temperatures, and a higher pressure at high temperatures.
Pure pyrotechnic gas generators comprise a housing, a pyrotechnic gas generating material, which may be a solid, a liquid, or a gas, an igniter for initiating combustion of the pyrotechnic gas generating material, and an outlet. The output of pyrotechnic gas generators is a hot gas, produced by the combustion of the pyrotechnic material, and has a temperature of at least about 1000xc2x0 C., which is near the limit of thermal acceptability in many applications. In addition, the housing of such devices becomes very hot during operation, as the combustion occurs within and in contact with the housing, heating the housing. Tortuous gas paths and/or heat sinks can be and are sued to reduce the temperature of the gas and the housing. As a result, however, pyrotechnic gas generators are heavy. In addition, pyrotechnic gas generators may require filters to remove particulates and heat from the gas stream in many applications, which also adds to the weight of the device. However, pyrotechnic gas generators are smaller and lighter than pressurized gas devices. Moreover, in most applications for propulsion devices, the temperature of the gas causes a rapid expansion of the gas, helping to provide thrust.
Because of deficiencies in cost, heat, toxicity, and performance, pure pyrotechnic gas generators are replaced with hybrid gas generators in some applications. Hybrid gas generators comprise a housing, containing a pyrotechnic material and a compressed gas, which is preferably inert, an igniter for initiating combustion of the pyrotechnic material, and a sealed outlet, which maintains the compressed gas within the housing, and opens to release the gas when the pressure of the gas is increased to a predetermined pressure upon heating of the gas by the combustion of the pyrotechnic material. Hybrid gas generators vary in performance, but the best provide a clean gas that is significantly cooler than that provided by pyrotechnic devices. The best hybrid gas generators for many applications are now less expensive than pyrotechnic devices, as a result of design improvements, and are now being installed in applications where pure pyrotechnic designs were typically used, such as, e.g., steering wheel air bag inflators.
As discussed above, gas generators have been shown to be useful in fire suppression, e.g., carbon dioxide and HALON(copyright) fire extinguishers. Fire suppression is typically achieved with the use of physical and/or chemical mechanisms to extinguish flaming and non-flaming or smoldering fires. The physical mechanism involves the physical displacement of oxidizer by the fire extinguishing composition and/or the absorption of an amount of heat sufficient to lower the temperature of the combusting materials below the ignition point by the molecules of a fire extinguishing composition, either of which terminates combustion. Generally, as the number of atoms in an extinguishment molecule increases the number of degrees of vibrational freedom also increases, and, thus, the heat capacity of the molecule increases, increasing the heat removal capacity of the extinguishment molecule. Physical suppression methods are most effective when directed at the base of the fire, where the fuel for the fire is typically located.
The chemical mechanism, on the other hand, involves interruption of the free radical fire-propagation chain reactions, which generally occur in the flames of a fire. The free radical fire-propagation chain reactions are the various reactions involving molecular oxygen and free radicals such as atomic hydrogen, atomic oxygen, and hydroxyl that often produce flame as well as the heat that keeps a fire burning. It has been speculated that halogen atoms, such as atomic bromine and iodine when present in sufficient numbers, disrupt these chain-propagation reactions, terminating both the chain reactions and combustion. Halides are ranked for their fire suppression capabilities, i.e., fluorine/fluorides are assigned a value of 1, chlorides 5, bromides 10, and iodides 16. That is, iodine is 16 times more effective than fluorine/fluorides. As a result, chemical suppression methods are generally most effective when directed into the flames of a fire where the free radical fire-propagation chain reactions occur and may be terminated.
A variety of agents and techniques are currently used for fire suppression, utilizing a chemical mechanism, a physical mechanism, or a combination of chemical and mechanical mechanisms. One conventional agent is pressurized water that extinguishes solely by thermal energy absorption. Water-based devices are not suitable, however, for use on electrical or flammable-liquid fires. Carbon dioxide, CO2, and dry-chemical extinguishers, now in use, typically displace oxygen and absorb thermal energy. However, dry-chemicals can leave a corrosive residue that is undesirable in many applications, such as electronic equipment. For use against grease fires, sodium bicarbonate extinguishers, potassium bicarbonate, urea-based potassium bicarbonate, and potassium chloride extinguishers are effective, but these can also leave a heavy powdered chemical residue that can damage electrical equipment. Yet another conventional fire extinguisher is the foam (AFFF or FFFP) model, which coats flammable liquids with a chemical to lower the temperature or to eliminate the oxygen supply, although these are not suitable for electrical fires [Nat""l Fire Protection Ass""n, 1995].
U.S. Army studies on halogenated agents in the 1940""s resulted in the adoption of the well known HALON(copyright) family of fire suppression compositions. HALONS are currently in use as highly effective fire suppression agentsxe2x80x94particularly in tanks, planes, ships, and heavy engines, notwithstanding that they are believed to be environmentally deleterious. Conventional halogenated agents, such as carbon tetrachloride and HALONS, e.g., bromotrifluoromethane, can provide both physical and chemical fire suppression mechanisms.
The HALONS are bromofluorocarbons (xe2x80x9cBFCsxe2x80x9d) that are similar to chlorofluorocarbons (xe2x80x9cCFCsxe2x80x9d) but have the formula CwBrxClyFz, where W=1 or 2, Y=0 or 1, and X+Y+Z=2W+2. HALONS must be sufficiently heated and pyrolyzed by the heat of a fire to produce free radicals before they achieve sufficient firefighting efficacy. Thus, HALONS are fairly stable and tend to work best on fires with hotter temperatures. This stability can result, however, in a fire suppression efficiency of only about 5 percent for HALONS. Moreover, because of their stability, these organic compounds tend to have long atmospheric lifetimes, and can migrate to the stratosphere where they are photolyzed by ultraviolet radiation, releasing chlorine or bromine atoms that catalytically remove ozone in a series of free radical reactions. Depletion of stratospheric ozone could allow an increase in the amount of ultraviolet light to reach the surface of the earth, resulting in increases in human skin cancer and cataracts, as well as damage to crops, natural ecosystems, and materials, and various other adverse effects. In addition, HALONS may also contribute to global warming. As a result, due to their potential to remove stratospheric ozone, conventional brominated agents and other volatile halogenated alkanes are presently being eliminated from worldwide production, pursuant to the adoption of the Montreal Protocol and the Clean Air Act of 1990.
The cost of perfluorocarbons is higher, and their fire fighting performance less effective, than those of the brominated agents. In weight and volume critical situations, such as aircraft, tanks, and ships, the additional quantity required for fire suppression is unacceptable. Perfluorinated agents also have high global warming potential (xe2x80x9cGWPxe2x80x9d) and atmospheric lifetimes estimated to be several thousand years. Therefore, their production and use is also restricted by legislation and liability concerns of current manufacturers.
In order to quantify these concerns, halogen-containing fire suppression agents are assigned an ozone-depletion potential (xe2x80x9cODPxe2x80x9d) that reflects their quantitative ability to destroy stratospheric ozone. The ozone depletion potential is calculated in each case relative to CFC-11 (CFCl3, trichlorofluoromethane), which has been assigned a value of 1.0. Many CFCs have ODPs near 1. HALONS have higher ODPs of between about 2 and about 14, indicating a greater ozone depletion potential. There is thus a need for fire suppression compositions that overcome the drawbacks of conventional agents as discussed above.
Firefighting compositions to replace HALONS should effectively suppress fire, be relatively nontoxic, electrically nonconductive, evaporate cleanly, and have low or no environmental impact. HALONS, although they meet the first four criteria, have long atmospheric lifetimes and high ozone-depletion potentials, and, thus, are being phased out of use, as discussed above.
Although it is relatively easy to identify fire suppressing agents having one, two, or three of these properties, it is very difficult to identify agents that simultaneously possess effective fire suppression performance, non-flammability, low toxicity, cleanliness, electrical non-conductivity, miscibility with common lubricants, short atmospheric and environmental lifetimes, low or no ODP, and very low GWP. Other characteristics are desirable, such as reduced toxicity, which is another major issue in the selection of firefighting agents. For example, the toxic effects of haloalkanes include simulation or suppression of the central nervous system, initiation of cardiac arrhythmia, and sensitization of the heart to adrenaline. Inhalation of gaseous haloalkanes can cause bronchoconstriction, reduce pulmonary compliance, depress respiratory volume, reduce mean arterial blood pressure, and produce tachycardia. Long term effects can include hepatotoxicity, mutagenesis, teratogenesis, and carcinogenicity.
Furthermore, firefighting agents must also be chemically stable during storage prior to use over long periods of time, such that they are not reactive with the containment system in which they are housed, and stable as well when stored at temperatures of about xe2x88x9220xc2x0 C. to about 100xc2x0 C., while decomposing at the higher temperatures in or near a fire to yield radical-trapping species.
A variety of alternative agents containing halides are known for fire suppression, although they are either less effective than HALONS or lack one of the characteristics desired in fire suppression agents as described above. Some of these methods and agents are discussed below. For example, one neat iodinated agent, trifluoroiodomethane, CF3l, has long been known to have firefighting potential [Dictionary of Organic Compounds, Chapman and Hall, N.Y., p. 5477 (1982)].
U.S. Pat. No. 2,818,381 discloses the use of methyl bromide for extinguishing fires. This reference also discloses another early fire extinguishing composition having 10-40 parts by weight of a chloro-difluoromethane with between one and two chlorine atoms and 90 to 60 parts by weight of a mixture of bromoform and ethyl bromide.
U.S. Pat. No. 3,779,825 discloses a solid propellant composition having 60 to 90 weight percent oxidizer component selected from solid inorganic oxidizing salts of ammonium perchlorate, the alkali metal perchlorates, ammonium nitrate, the alkali metal nitrates, and mixtures thereof, at least a major portion of the oxidizer being of the perchlorates; from 10 to 40 weight percent of a binder of a rubbery material; and from 0.1 to 8 weight percent of a burning rate depressing agent.
U.S. Pat. No. 4,406,797 to Altman et al. discloses a fire extinguishing composition having a mixture of finely divided aluminum compound and an alkali metal, stannous or plumbous halide. The metal halide may include an alkali metal, e.g., potassium iodide, bromide, or chloride, or stannous or plumbous iodide, bromide or chloride, although potassium iodide is disclosed to be preferred for use in the composition.
U.S. Pat. No. 5,466,386 to Stewart et al. discloses fire-extinguishing compositions of low ozone depletion potential having dry particles of ammonium bromide coated with a water repelling, solid, non-flammable adherent, such as zinc stearate, to improve flowability. The particles allegedly enhance the fire-extinguishing properties of chlorofluorocarbons and halogenated paraffins having low ozone depletion properties when dispersed therein.
U.S. Pat. No. 5,520,826 to Reed, Jr., et al. discloses a fire extinguishing pyrotechnic having an azido binder, such as a glycidyl azide polymer (GAP), an azido plasticizer, a solid tetrazole, and a perfluorocarboxylic acid salt cured to a rubbery composite by the addition of an isocyanate that flamelessly deflagrates to produce primarily nitrogen, carbon dioxide, and a fluoroolefin.
U.S. Pat. No. 5,562,861 to Nimitz et al. discloses a set of environmentally safe, nonflammable, low-toxicity refrigerants, solvents, foam blowing agents, propellants, and firefighting agents that allegedly have no ozone-depletion potential. These agents include at least one fluoroiodocarbon agent of the formula CaHbBrcCldFeIfNgOh, where a is 1 to 8; b is 0 to 2; c, d, g, and h are each 0 to 1; e is 1 to 18; and f is 1 to 2. This reference also notes that conventional chemical wisdom indicates that iodine-containing organic compounds are too toxic and unstable to use for these purposes, and iodocarbons have been rejected on those grounds by the majority of those skilled in the art.
U.S. Pat. No. 5,626,786 to Huntington et al. discloses a class of fire suppressant compounds having labile bromine atoms bound to non-carbon atoms that are alleged to be more effective than HALON(copyright) 1211 and 1301 at suppressing fires. These compounds are disclosed to hydrolyze or oxidize rapidly in the troposphere, thereby having minimal ODP.
U.S. Pat. Nos. 5,861,106 and 6,019,177 to Olander disclose compositions and methods for suppressing fires using the disclosed compositions, where the compositions comprise an organic binder, having a heat of formation of less than about 200 cal/g, and an inorganic halogen containing component, such as potassium or ammonium bromide, bromate, iodide, or iodate.
U.S. Pat. No. 5,449,041 to Galbraith discloses an apparatus and method for suppressing a fire that is less environmentally hazardous than the use of Halon(copyright). A gas generator is used to produce a first gas at an elevated temperature containing carbon dioxide, water vapor, and/or nitrogen. The first gas is then used to vaporize a liquid, such as water, liquified carbon dioxide, or a fluorocarbon, to produce a gas having fire suppressing capabilities.
Reduction of toxicity, ODP, and other environmental effects must be balanced against effective fire suppression to achieve a superior fire suppression composition and method. Although more recent fire suppression compositions, such as those disclosed by Olander, have significantly reduced ozone depletion potential, improvements in fire suppression effectiveness are still desirable. Therefore, a need exists for improved devices and methods for delivering an environmentally-friendly, nontoxic fire suppressant that provides better fire suppression effectiveness than presently available fire suppression devices and agents. The present invention clearly meets this long-felt need in the manner and for the reasons described herein.
The invention is directed to gas generating devices, such as e.g., inflators, propulsion devices, and fire suppression devices. In a first embodiment, the gas generating devices of the invention comprise a first stage gas source and a second stage gas source. The first stage gas source has an outlet, and contains a pyrotechnic gas generating material, which, upon combustion, produces a quantity of gaseous combustion products. Optionally, the first stage gas source contains a compressed gas.
The second stage gas source contains at least one of a liquefied gas or supercritical carbon dioxide, is in fluid communication at a first location with the outlet of the first stage gas source, and comprises an outlet for dispersing gas. The first and second stage gas sources are configured and adapted such that, upon release of gas from the outlet of the first stage gas source at the first location, at least a portion of gas produced by the first stage gas source is introduced into the second stage gas source at a location within the liquefied gas or supercritical carbon dioxide. The first stage gas source is capable of providing a sufficient quantity of gas at a sufficiently high temperature to vaporize at least a portion of the liquefied gas or increase the pressure of the supercritical carbon dioxide in the second stage gas source, thereby increasing the pressure within the second stage gas source, and releasing gas from the outlet of the second stage gas source.
Where the first stage gas source is a hybrid gas generating device, the first stage further comprises a first stage housing defining a first interior volume, and having an inner surface, and contains a pressurized gas at a first pressure in the first interior volume. An igniter in thermal contact with the pyrotechnic material is used for initiating combustion of the pyrotechnic material, and a first stage seal seals the first stage outlet. The first stage seal is adapted to maintain the pressurized gas at the first pressure within the first interior volume, and to open when the gas attains a predetermined second, higher pressure upon combustion of the pyrotechnic material located within the first stage housing to allow the gas to pass from the first stage housing through the first stage outlet into the second stage gas source.
The second stage gas source preferably comprises a second stage housing defining a second interior volume, an inlet, and gas directing means for directing a quantity of gas from the first stage gas source to a predetermined location within the second stage gas source, where the inlet is in fluid communication with the outlet of the first stage gas source and the gas directing means to allow gas to pass from the first stage gas source to the predetermined location within the second stage gas source.
Preferably, the gas directing means comprises at least one metering tube, extending within the interior volume of the second stage housing from the second stage gas source inlet to direct gas from the first stage gas source into the interior volume of the second stage gas source. The at least one metering tube is preferably adapted to direct the gas from the first stage gas source to a location within the interior volume of the second stage housing proximate to the inlet of the second stage gas source.
Wherein the second stage gas source contains a liquefied gas, the liquefied gas preferably comprises at least one of nitrogen and carbon dioxide, and, more preferably, comprises carbon dioxide and up to about 25 mole percent nitrogen.
Useful pyrotechnic gas generating materials comprise a nitrate or perchlorate oxidizer and an energetic fuel, such as, e.g., RDX, HMX, CL-20, TEX, NQ, NTO, TAGN, PETN, TATB, TNAZ, and mixtures thereof.
When the gas generating device is adapted for use as a fire suppressing device, at least one of the pyrotechnic gas generating material and the liquefied gas or the supercritical carbon dioxide is mixed with or includes at least one fire suppressant material selected from the group consisting of elemental halogens and alkali metal halides, where the fire suppressant material is preferably at least one of elemental iodine and potassium bromide. Preferably, the fire suppressant material is coated or encapsulated with a protectant material adapted to prevent reaction of the fire suppression material with the pyrotechnic material, liquefied gas, or supercritical carbon dioxide. Suitable coatings include, but are not limited to epoxies, polyurethanes, polyesters, and cellulose acetate.
The pyrotechnic gas generating material preferably comprises a pyrotechnic fire suppression material, such as those disclosed in U.S. Pat. Nos. 5,861,106 and 6,019,177 to Olander. Such fire suppression materials comprise an inorganic halogen-containing component and an organic binder system, and may further comprise an elemental halogen, such as iodine. The inorganic halogen-containing component is preferably selected from the group consisting of potassium bromide, potassium bromate, potassium iodide, potassium iodate, ammonium bromide, ammonium bromate, ammonium iodide, ammonium iodate, and mixtures thereof. In addition, the organic binder preferably has a heat of formation of less than about 200 cal/g. Such as pyrotechnic fire suppression composition is solid at a temperature below 100xc2x0 C., when cured, and combusts at a temperature between about 160xc2x0 C. to 1200xc2x0 C. to produce one or more reaction products that suppress fire, such as , e.g., H2O, CO, Kl, KBr, H2, COH2, O2, I2OH, K2l, and mixtures thereof.
The organic binder system comprises a binder resin of at least one curing binder, melt cast binder, solvated binder, or a mixture thereof, a curative present in about 1 to 3 weight percent, and a plasticizer present in about 10 to 30 weight percent, based on the total weight of the binder system, where the organic binder system has a heat of formation of less than about 200 cal/g. Preferably, the binder resin is selected from the group consisting of carboxy-terminated polybutadiene, polyethylene glycol, polypropylene glycol, hydroxy-terminated polybutadiene, polybutadiene acrylonitrile, polybutadiene acrylic acid, butacene, glycol azido adipate, polyglycol adipate, and mixtures thereof. The organic binder system may further comprise at least one of a curing or bonding agent, an antioxidant, an opacifier, and a scavenger.
In a further embodiment, the invention is directed to a gas generating device, adapted for producing a sufficient quantity of a gaseous fire suppressing material to substantially suppress a fire. The device comprises a first stage gas source containing a pyrotechnic, gas generating, fire suppression composition, which, upon combustion, produces a fire suppressing gas, and, optionally, a pressurized gas, where the pyrotechnic, gas generating, fire suppression composition comprises an inorganic halogen-containing component, an organic binder system, and at least one elemental halogen. Preferably, the at least one elemental halogen is elemental iodine or elemental bromine, which is more preferably coated or encapsulated with a protectant material adapted to prevent reaction with the pyrotechnic composition.
The inorganic halogen-containing compound is preferably present in an amount of from about 70 to 96 weight percent and the organic binder system is present in an amount of from about 4 to 30 weight percent, based on the total weight of the pyrotechnic composition, and the inorganic halogen-containing component is preferably selected from the group consisting of potassium bromide, potassium bromate, potassium iodide, potassium iodate, ammonium bromide, ammonium bromate, ammonium iodide, ammonium iodate, and mixtures thereof. More preferably, the organic binder has a heat of formation of less than about 200 cal/g, and wherein the pyrotechnic fire suppression composition is solid at a temperature below 100xc2x0 C., when cured, and combusts at a temperature between about 160xc2x0 C. to 1200xc2x0 C. to produce one or more reaction products that suppress fire, such as, e.g., H2O, CO, Kl, KBr, H2, COH2, O2, I2OH, K2l, and mixtures thereof.
The organic binder system preferably comprises a binder resin of at least one curing binder, melt cast binder, solvated binder, and a mixture thereof, a curative present in about 1 to 3 weight percent, and a plasticizer present in about 10 to 30 weight percent, based on the total weight of the binder system, where the organic binder system has a heat of formation of less than about 200 cal/g. The binder resin is preferably selected from the group consisting of carboxy-terminated polybutadiene, polyethylene glycol, polypropylene glycol, hydroxy-terminated polybutadiene, polybutadiene acrylonitrile, polybutadiene acrylic acid, butacene, glycol azido adipate, polyglycol adipate, and mixtures thereof. The organic binder system may further comprise at least one of a curing or bonding agent, an antioxidant, an opacifier, and a scavenger.
Preferably, the gas generating device further comprises a second stage gas source in fluid communication at a first location with the first stage gas source, the second stage gas source comprising an outlet, and containing at least one liquefied gas or supercritical carbon dioxide, where the first stage gas source is capable of directing a sufficient quantity of gas at a sufficiently high temperature through an outlet therein and into the liquefied gas or supercritical carbon dioxide within the second stage gas source to vaporize at least a portion of the liquefied gas or supercritical carbon dioxide in the second stage gas source. As a result, the resulting gas exits the second stage gas source through the second stage outlet and is directed at the fire. Preferably, a halogen, such as iodine, is dissolved in the liquefied gas or supercritical carbon dioxide.
The invention is further directed to method for generating gas using a gas generating device of the invention. The method comprises initiating combustion of a pyrotechnic gas generating material located within a first stage gas source, introducing gas from the first stage gas source into a liquefied gas or supercritical carbon dioxide within a second stage gas source in fluid communication with the first stage gas source, where the first stage gas source provides a sufficient quantity of gas at a sufficiently high temperature to vaporize at least a portion of the liquefied gas or to cause an increase in pressure of the supercritical carbon dioxide, and at least a portion of the gas introduced into the liquefied gas or supercritical carbon dioxide in the second stage gas source is produced by the combustion of the pyrotechnic gas generating material, vaporizing at least a portion of the liquefied gas or increasing the pressure of the supercritical carbon dioxide with the gas from the first stage gas source sufficiently to cause a release of gas from the second stage gas source and releasing an output gas from the second stage gas source through an outlet therein, the output gas comprising the vaporized gas from the second stage gas source.
The method may further comprise providing a first stage housing adapted to contain the pyrotechnic material, the housing defining a first interior volume, and having an inner surface, the first stage housing containing a pressurized gas at a first pressure in the first interior volume, and the housing having a seal adapted to maintain the pressurized gas at the first pressure within the first interior volume, and to open when the gas attains a predetermined second higher pressure, and burning the pyrotechnic material located within the housing to generate heat, thereby increasing the pressure of the pressurized gas to at least a second higher pressure to allow the gas to pass from the housing.
The method of the invention preferably comprises providing a second stage in fluid communication with the first stage, the second stage comprising a second stage housing defining a second interior volume, an inlet adapted for fluid communication with the first gas source, an outlet, and, optionally, at least one metering tube in fluid communication with the inlet and extending within the interior volume of the second stage housing for introducing the gas from the first stage gas source into an interior volume of the second stage gas source. Gas from the first stage gas source is introduced within the liquefied gas or supercritical carbon dioxide within an interior volume of the second stage gas source.
When the invention is adapted for fire suppression, the output gas from the second stage gas source into flames from a fire or onto a source of fire, thereby suppressing the fire. Preferably, at least one fire suppressant material selected from the group consisting of elemental halogens and alkali metal halides is added to at least one of the pyrotechnic material and the liquefied gas or supercritical carbon dioxide, where the at least one fire suppressant material is coated, encapsulated, or microencapsulated with a protectant material to prevent reaction with the pyrotechnic material. To enhance the fire suppression capability of the invention the gas released by the first stage gas source may be produced from the combustion of a pyrotechnic fire suppression composition, such as those discussed above.
In a further embodiment, the invention is directed to a gas generating device having multifunctional capabilities. The gas generating device comprises a first stage gas source comprising a housing defining an interior volume, the housing containing a pyrotechnic material for producing at least one of heat and gas upon combustion, an igniter for initiating combustion of the pyrotechnic material upon receipt of an initiation signal, a first stage outlet, a first stage outlet seal adapted for sealing the first stage outlet, and a first stage outlet seal opening means for opening the first stage outlet seal upon receipt of an actuation signal to allow the gas to flow from the first stage housing through the outlet, a second stage gas source in fluid communication at a first location with the first stage gas source, and having a second stage outlet at a second location, the second stage gas source containing at least one liquefied gas or supercritical carbon dioxide, and having a second stage outlet seal adapted to maintain the at least one liquefied gas or supercritical carbon dioxide within the second stage, and to open upon receipt of either an actuation signal by a second stage outlet seal opening means operatively associated with the second stage outlet seal or upon an increase in pressure within the second stage to a predetermined second stage gas pressure, to allow gas to flow from the second stage housing, and a third seal at the first location between the first and second stage gas sources adapted to open when pressure within the first stage gas source attains a predetermined first stage gas pressure upon combustion of the pyrotechnic material to allow gas from the first stage gas source to enter the second stage gas source. The first stage gas source is capable of providing a sufficient quantity of gas at a sufficiently high temperature to vaporize at least a portion of the liquefied gas or supercritical carbon dioxide in the second stage gas source.
The gas generating device may further comprise a pressurized gas at a storage pressure in the interior volume of the first stage gas source, where the first stage outlet seal and the third seal are adapted to maintain the pressurized gas at the storage pressure within the interior volume prior to combustion of the pyrotechnic material.
To generate a gas with the multifunctional gas generating of the invention, at least one of the igniter, the first stage outlet seal opening means, and the second stage seal opening means is actuated to release a gas from at least one of the first stage gas source and the second stage gas source. For example, initiation of combustion of the pyrotechnic material using the igniter produces a first gas pressure within the first stage gas source of at least the predetermined first stage gas pressure. As a result, the third seal between the first and second stage gas sources open, introducing the gas from the first stage gas source into the second stage gas source, thus vaporizing the liquefied gas or supercritical carbon dioxide within the second stage gas source. The introduction of gas from the first stage into the second stage produces a second gas pressure within the second stage of at least the predetermined second stage gas pressure to open the second stage outlet seal, thereby opening the second stage seal, and releasing a gas comprising gas from the first stage gas source and gas from the second stage gas source through the second stage outlet Alternatively, the igniter may be used to initiate of combustion of the pyrotechnic material, producing a gas pressure within the first stage gas source less than the predetermined first stage gas pressure, and actuating the first stage outlet seal opening means, thus opening the first stage outlet. Similarly, the second stage outlet seal opening means may be actuated, opening the second stage outlet, and allowing a gas to flow from the second stage gas source through the second stage outlet.
The invention may be used to suppress a fire using the multifunctional gas generating device described above by actuating at least one of the igniter, the first stage outlet seal opening means, and the second stage seal opening means to release a fire suppressing gas from at least one of the first stage gas source and the second stage gas source, and directing the fire suppressing gas at a source of fire, thereby suppressing the fire.